Coating remover composition



ZDZ'I U United States Patent 3,138,556 COATING REMOVER COMPOSITION Henry A. Goldsmith, Torrance, and Robert B. Roessler,

Rolling Hills Estates, Calif., assignors to Purex Corporation, Ltd., South Gate, Calif., a corporation of California No Drawing. Filed Sept. 5, 1961, Ser. No. 135,726 15 Claims. (Cl. 252-136) This invention relates to compositions useful in the removal or stripping of aints 0 tin and is especimfiWy effective in the removal of chemically resistant coatings and paints such as those based on e oxy resins.

During recent years, very adherent, durable paints and coatings based upon chemically resistant resins have been developed, owing to the superior properties of these paints or coating compositions over the conventional lacquers and paints. However, because of the tenacity and durability of certain coatings based on such resins, and particularly on certain epoxy resins cured by incorporation of amine catalysts, there has been a problem of developing means for removing or stripping such obdurate coatings and paints rapidly and effectively from surfaces to which they have been applied, for example, from defectively coated parts or parts which it is desired to repaint. Although strippers have been developed for this purpose, they have not proven entirely satisfactory from the standpoint of rapid removal of certain of these coatings and freedom from adversely affecting or damaging the substrate, particularly where the substrate is aluminum, magnesium or steel. Many prior art compositions require several hours or more for complete stripping of chemically resistant coatings, While others requiring a shorter period for this purpose are too corrosive to the substrate, especially where the latter is magnesium, aluminum, or steel.

It is an object of this invention to provide novel coating or paint stripping compositions having superior effectiveness for removing obdurate coating compositions such as those based upon epoxy resins.

Another object of this invention is the provision of novel paint and coating strippers effective for removing chemically resistant paints or coatings within a relatively short period, for example, in less than 3 hours, and preferably less than about 2 hours.

Still another object is the provision of novel paint and coating strippers effective for removing obdurate paint or coatings rapidly, and which during their period of application are substantially non-corrosive to the substrate, particularly aluminum, magnesium or steel.

Yet another object is the design of non-flammable stripping compositions having the aforementioned characteristics.

A still further object is to afford paint strippers of the nature noted above, which have good stability and which can be applied either by immersion of the part in the composition, or by spray, brush or similar application to the coated surface of the part.

Still another object is the provision of procedure for removal of obdurate paints and coatings such as those based on epoxy resins, employing the aforementioned types of stripping compositions.

Other objects and advantages of the invention will appear hereinafter.

In application Serial Number 135,727 of Arden and Roessler, filed of even date herewith, it is disclosed that when hypophosphorous acid (H PO is incorporated into stripping compositions con aimng a substantial proportion of chlorinated hydrocarbon solvent, preferably methylene chloride, and preferably also containing water and a lower alcohol, the effectiveness of the composition for Cross REFERENCE removing paint and coatings based on epoxy resins, is materially improved over prior art compositions containing in place of hypophosphorous acid, other activators such as ammonia, amines, organic acids, e.g., aliphatic acids, and phenols.

It has now been found that the epoxy stripping effectiveness of the hypophosphorous acid is materially fur ther enhanced by incorporating, together with th e hypophosphorous acid, an or anic activator compound for hypophosphorous acid, prefera5ly c ertain classes of organic activators, namely, alkyl phosphites, and hydroxylated SlX membereF ox en heterocyclic com s. Although the latter compounds are preerred over the alkyl phosphites, we have found that the alkyl phosphites function in substantially the same manner as the other organic compounds mentioned, all acting as activators for hyphosphorous acid.

Thus, employing hypophosphorous acid and such organic activators in stripping compositions according to the invention, coating systems of the most tenacious and durable nature, such as those composed of amine catalyzed epoxy resins can be stripped from the adjacent sub strate in a substantially reduced period of less than 3 hours, often in less than 1 /2 hours, as compared to conventional strippers for this purpose, which even if they strip at all, may require, for example, 10 hours or more for stripping such coatings.

It is believed that the stripper containing chlorinated hydrocarbon, e.g., methylene chloride, functions in the nature of a penetrating and swelling agent which causes the coating to swell or expand and thus detach itself from the surface to which it is applied, and that the hypophosphorous acid and its coactivators have an efficient activating effect on this penetrating and softening action by which they assist the chlorinated hydrocarbon to pass through the coating. The hypophosphorous acid and its coactivator particularly appear to have a bond releasing function which aids in breaking the bond holding the coating to the substrate. As a result of the combined effect of the chlorinated hydrocarbon, the hypophosphorous acid, and its coactivator, the expanded softened coating can be stripped or rinsed from the surface of the part in a minimum period of time. The superior action of hypophosphorous acid in paint stripping compositions of the char acter described herein, over other acids tested, including the related phosphoric and phosphorous acids, indicates that such superior effectiveness may be related to the reducing action of hypophosphorous acid, in addition to that of its acidity. However, the invention is not to be taken as limited by any theory of the function of the hypophosphorous acid and its coactivators in the paint stripping compositions of the invention.

Representative of alkyl phosphites which can be employed as organic activators in combination with bypophosphorous acid, we can employ dialkyl hydrogen phosphites and trialkyl phosphites containing lower alkyl where X is a member of the group consisting of ECOH,

EXAMINER 3 EC-OCHg, E-COOH and -O radicals, and derivatives thereof. Examples of such compounds are pmethoxy phenol (p-hydroxy anisole), marketed technically pure as Ansul HA, salicylic acid, hydroquinone, resorcinol, kojic acid, and the like. These compounds have the following structural formulae:

0 Hg 0 H I OH C 0 OH H OH pmethoxy salicylic hydrophenol acid quinone OH )-omon resorcinol kojic acid Of the above compounds, p-methoxy phenol, kojic acid and salicylic acid have been found to produce best results, in decreasing order of effectiveness, p-methoxy phenol having been found to be most effective.

It has been found that the above alkyl phosphites and aromatic and heterocyclic activators function, together with the hypophosphorous acid, in a synergistic manner to enhance materially the paint removing characteristics resulting from the use of the hypophosphorous acid. Thus, said activators when employed alone, that is, in the absence of hypophosphorous acid, are substantially of no greater effectiveness than many other compounds,

such as phenols, previously employed as activators, and may require, for example, in excess of five hours for stripping. On the other hand, the effectiveness of hypophosphorous acid, that is, its ability to remove certain resistant coatings such as epoxy coatings, in a period of the order of about 3 hours when employed in a stripper composition including a chlorinated hydrocarbon, can be markedly improved by incorporating therewith an organic activator as described above, so that, for example, the stripping time for removing the same type of coating can thus be reduced to as little as one and a half hours or less. Also, by employing such organic activators in combination with hypophosphorous acid in such paint stripping compositions, the amount of hypophosphorous acid employed can be reduced substantially, to obtain stripping in the same period of time as when employing a stripper containing a much larger amount of hypophosphorous acid and in the absence of the above organic activator.

An additional important advantage of the use of the above organic activators in combination with the hypophosphorous acid is, that in addition to increasing the rapidity-of stripping of the resistant coating, they tend to decrease the corrosiveness of the composition on magnesium, aluminum and steel parts to which the coatings are applied.

The amount of hypophosphorous acid which can be employed can vary in the range of about 0.25 to about 15% by weight of the composition, and preferably is in the range of about 1 to about an optimum quantity being about 4% by weight. Amounts larger than about 10% by weight are not favored, since this increases corrosive effects on magnesium and aluminum parts and decreases stability of the composition. Use of insufficient hypophosphorous acid does not effectively aid in decreasing stripping time. Hypophosphorous acid is preferably employed in the form of the commercially available 50% aqueous solution, although aqueous solutions of other concentrations can be employed.

The amount of organic activator described above may be employed in the range from about 0.25 to about 10% by weight of the composition, and usually from about 0.25 to about 3% by weight, with from about A to 2% being optimum, particularly in the case of the alkyl phosphites, p-hydroxy anisole, and kojic acid. Where salicylic acid is employed the proportions used range preferably from about 1 to about 6% by weight.

The chlorinated organic solvent used in our composition is exemplified by methylene chloride, ethylene dichloride, trichloroethylene, methyl chloroform, propylene dichloride, perchloroethylene, 1, 2, 4 trichlorobenzene and orthodichlorobenzene. All of these chlorinated materials are liquids throughout the entire range of operating temperatures normally employed with the compositions of the invention. The choice of the particular chlorinated organic solvent used is influenced by the operating temperature for which a particular coating stripping composition is formulated. Thus, the low boiling chlorinated aliphatic hydrocarbons noted above are preferably employed in compositions which are designed to be used at or near room temperatures, while chlorinated benzene derivatives, such as orthodichlorobenzene, are primarily suitable for use in compositions which are designed to be used at elevated temperatures. In general, the quantity of the chlorinated organic solvent is varied to accommodate other ingredients, but will normally be present in amounts generally in the range of about 40 to about preferably about 50 to about 70% by weight of the total composition.

Because of the corrosive nature of hypophosphorous acid on metals such as aluminum, magnesium and steel, it is generally preferred to incorporate suitable amounts of corrosion inhibitors into the composition. The in hibitors so employed should be of a nature which produce maximum corrosion inhibiting effect on the metal part from which the coating is being stripped, without adversely affecting the function of the hypophosphorous acid, and/or the organic activator; in other words, substantially without decreasing the rate of coating removal. We have found that a number of corrosion inhibitors give good inhibition while permitting rapid stripping. These include among others, for example, the ampholytic surface active compounds (1) oleyl ethyl cycloimidinium l-hydroxy, 3-ethyl sodium alcoholate, 2-methy1 sodium carboxylate (marketed as Miranol OM-SF), (2) N-alkyl amino sodium propionate, the alkyl group containing from 12 to 14 carbon atoms (marketed as .Deriphat 151), and oleyl sarcosine (marketed as Sarkosyl 0). By proper use of inhibitors such as those noted above, the attack of the coating stripper of the invention upon metals such as magnesium, aluminum and steel, and their alloys, can be materially reduced with little, if any, adverse effect on the stripping effectiveness of the composition. Generally, about 0.1 to about 2%, preferably about 0.3 to about 1.5% of the inhibitor or combination of inhibitors are employed based on the weight of the composition.

The presence of minor amounts of water in the epoxy shipping composition of the invention is of importance in reducing the stripping time. Thus an amount of water for this purpose in the range of about 0.25 to as high as about 15 and preferably from about 0.25 to about 5%, is utilized. If an amount of water greater than about 15% is employed, this tends to increase stripping time. The water employed in the composition may be introduced as such or may be introduced together with one or more of the other components of the composition. For example, it is convenient to employ a commercially available 50% aqueous hypophosphorous acid solution, the use of this latter material introducing all or part of the required amount of water into the composition.

In order to improve the compatibility of the water with the chlorinated hydrocarbon, e.g., methylene chloride, employed in the composition, it has been found useful to use a coupling agent. The coupling agent functions as a mutual solvent for the water and the chlorinated hydrocarbon such as methylene chloride. Examples of coupling agents which can be employed include lower aliphatic alcohols such as methanol, ethanol and isopropanel, and their glycol ethers, such as the methyl, ethyl or butyl ethers of ethylene, diethylene or propylene glyof small amounts of high molecular weight alcohols such as ethylhexanol and pineoil, as well as high molecular weight glycols such as hexylene glycol. The amount of wax or other evaporation retardant aid which can be employed may vary from about 0.1 to about 3% by C421, thle1 preferred material being methanol. The amount 5 i ht f th mpositi Sue Coupling agent p y y range from about Where the stripper of the invention is to be applied 3 to about 20%, preferably about 5 to about 15% by to obdurate coatings on inclined or vertical surfaces it Welght 0f the composition- It s b found that f is usually advantageous to incorporate in the composithe absence of such coupling agent the aqueous phase is tion a thickening agent to confer thixotropic properties not rendered fully active in the chlorinated hydrocarbon t h composition Minor amounts of i l i k. and the results are not as effec e as when p y g eners confer upon the composition a sutficient viscosity such couphng agent. such as that in the range of about 200 to about 800 cen- Varwus surface fi agents which are substantligly tipoises. A preferred material for this purpose is methyl stable to p p p owns acid r to y of the or er cellulose, e.g., the brand marketed as Methocel. Howihgfediehts 0f the composition including the Organic e ever, other suitable materials may be employed for this VatOI'S, are also h' ye p y in the eofflposltlohs purpose. The amount of thickening agent generally emaccording to the invention. A surface active agent l d may range from b t ()5 t b t 3% by weight fTohuncli particularlylsuitable is 1marketlflcg astPetronate f h composition h e fitter materia is a Petro cum 5 ohae compost The followin example shows a comparison of t e Composed of about 62% Petroleum Sulfonate, believed 3 effectiveness for stripping a highly tenacious durable type be of the approximate Composition 26 42 3 an of epoxy coating, as between compositions containing d g g molecular Weight Of 457, 33% mineral Oil, acids other than hypophosphorous agid, t:zompositions an 0 Watercontaining hypophosphorous acid in t e a sence of an It has been found that thi Surface aetlve agent D organic activator, and compositions containing both hy- Satisfactory Water l'hlsahilitys Penetratloh, Shelf pophosphorous acid and an organic activator, according bility to the composition, and aids in inhibiting corroto h invention sion, particularly on aluminum and magnesium alloyas. A LE 1 However other acid-stable surface active agents can e E h th tio belo wa test d for stri employed an exampie of another Such wetting agent in effezhve e 2 1 1 saii i le of 202j aluihinum allcFy being Nacconol Z which is an 85% alkyl z ne u hr t t o gersio coatin for ed th r nate having an average of 12 carbon atoms in the alkyl avlilg c d mil m at 3 chain. Alkyl aryl sulfonates having, for example, 9 to F a W S t al Z3 1e 1 resin g ii whicl; 15 carbon atoms in the alkyl chain can be employed. g g gg i coatbas d o amine The amount of surface active agent which can be em- 35 a the allele w baked ployed can vary in the range from about 2 to about 10% ca f epoxy e l me p S e e by weight of the composition at 200 F. for about 1 hour. The unbaked panels so Also preferably, but not necesarily, employed in the coated were treated wnhFach of comPostlonsb i invention composition are evaporation retardants. The 17 Table I below whlle the f s gf a 6 function of these materials is to maintain the composi 40 Coatlhgs thereon were treated W1th Composmon? 18 to tion unchanged after it has been sprayed or poured on a h treatment was earned out y PP Y g the floating, by holding egaporatitctiln of 21; efssential ingrhe- P gpp l s thp h Wlth t Pane1 pl t th ients to a minimum uring e pen 0 stripping e or a a ang e. ripping was ra e as comp e e w en coating. Generally, waxes, for example, paratfin wax the blue epoxy paint coating had swelled and blistered and microcrystalline wax, are employed for this purpose. and could be rinsed off with little or no wiping. The The action of such waxes is assisted by the incorporation compositions and results are given in Table I below:

Table l COMPOSITIONSPERCENT BY WEIGHT Methylene chloride Methyl alcohol Paratfin wax.

Hypophosphorous acid aqueous solution) Formlc acid (90% aqueous solution) Glycolic acid aqueous solution) NacconolZ Petronate HL p-Methoxy nhpnnl Kojic acid Salicylic acid- Rcsorcinol Triisopropyl phosphite Tricresyl phosphite D butyl hydrogen phosphite- Dime'tliyl hydrogen phosphi Trimethyl phosphite Tributyl phosphite Time in hours required for complete stripping 1 No effect. 1 Min.

It is seen from Table I above that compositions 4, and 6, containing no hypophosphorous acid, were ineffective to cause stripping of the epoxy coating except after many hours of treatment. It is particularly noteworthy that this was true for Composition 6, which although it contained kojic acid, one of the organic activators of the invention, did not contain the other essential component, hypophosphorous acid. Composition 7 containing hypocoating as in Example 1. The compositions and results are given in Table II below. It is noted that the weight change of each specimen due to corrosion is given in terms of a loss or gain in weight. The weight change is given as a loss (negative) where metal was actually removed, and the weight change is given as a gain (positive) where the effect of corrosion was to form a coating and thus adding weight to the specimen.

Table II Formulation (Remainder of each formulation is methylene CorrosionLoss or gain per 4 square chloride)percent by weig t inch panel in 24 hours Inhibitor Ha z Epoxy 50% 0113011 2-cthyl Petro- Activator strip Dow 7 2024 1020 Aq. Sol. hexanol nate HL time Mg A1 steel (min.)

8 12 4 1.5% kojic acid 120 129. 7 80. 8 5. 4 8 12 4 d0 0.5% Deriphat 151 135 76.1 1. 2 8 12 4 do 0.5% Sarkosyl O 90 3. 3 36.3 -1. 8 8 12 4 1.5% p-hydroxy- 150 154. 34 513. 7 11.9

anisole (=HA). 8 12 4 1.5% H- 0.5% Deriphat151.. 90 40.1 74. 9 0.8 8 8 4 4 1.5% II do 115 41. 6 40. 1 6. 6 8 8 4 4 1.5% HA 0.5% Sarkosyl O 60-80 39. 6 104.8 7. 1 8 4 4 1.5% HA 1% Miranol 0MSF 130 6.9 -120. 8 8 12 4 1.5% Tricresyll 80135 94.7 117.8 7 5 phosphite (=TCP). 8 8 4 4 1.5% 01? 0.5% Deriphat151 110 -51. 4 52. 3 6. 2

phosphorous acid, but in the absence of the above described organic activator, stripped these obdurate amine catalyzed epoxy coatings in a period of 3.5 hours.

However, Compositions 8, 9, 10, 11, 18 and 19, containing the combination of hypophosphorous acid and the preferred organic activators p-methoxy phenol or kojic acid, singly, or in combination as in Composition l1, resulted in complete stripping of these tough epoxy coatings in a period of from under 1 hour-Composition 10, to about 1.5 hours. Compositions containing hypophosphorous acid and either salicylic acid or resorcinol Compositions 12 and 13, required from about 1.5 to about 2 hours to accomplish stripping.

Stripping compositions according to the invention, containing hypophosphorous acid and alkyl phosphite as the organic activator, were also superior in their stripping effectiveness to hypophosphorous acid alone, but not as stable on storage as the preferred compositions containing hypophosphorous acid and, for example, p-methoxy phenol or kojic acid as activators. Freshly made Compositions 14, 15, 16, 17, 20 and 21, representative of this class of invention compositions, required about 2 to 2.5 hours to accomplish stripping.

The following example shows the corrosion inhibiting effectiveness on Dow 7 magnesium, 2024 aluminum and 1020 steel, of certain inhibitors when employed in the invention composition containing hypophosphorous acid and certain of the organic activators described above, for stripping an epoxy coating from the surface of such metals.

EXAMPLE 2 Into each of the compositions listed in Table H below was placed one each of three test panels of Dow 7 magnesium, 2024 aluminum and 1020 steel, respectively, each panel having four square inches of surface area. Each panel was immersed for a period of 24 hours in the respective compositions, which were maintained at room temperature. Corrosion, expressed as the loss or gain in weight, in milligrams, of each of the panels was observed at the end of the 24 hour period. Independently, the time was observed for stripping of baked epoxy coatings from 2024 aluminum primed with chromate conversion From Table II above, it is seen that in formulations employing kojic acid as organic activator, the incorporation of Sarkosyl 0 into the composition as inhibitor sub stantially reduced corrosion on all three types of metal panels as compared to the control not including the inhibitor, while the incorporation of Deriphat 151 was effective on Dow 7 magnesium and 1020 steel, and such inhibitors did not unfavorably affect stripping time. Sarkosyl O is noted as particularly effective on Dow 7 magnesium.

As to formulations containing p-hydroxy anisole, each of the four inhibitors tested therewith decreased corrosion on all three types of panels.

With respect to formulations containing tricresyl phosphite as organic activator, the use of Deriphat 151 as inhibitor was effective in decreasing corrosion on all three types of panels, and did not adversely affect stripping time to any material extent.

Hence it is seen that each individual inhibitor has a somewhat different effect when incorporated in the various invention compositions, depending on the type of organic activator employed and the particular base metal of the substrate on which the epoxy coating is applied.

EXAMPLE 3 The following are examples of particularly efiective stripping compositions which have been found to strip the most durable type of epoxy coatings in a period of about 1.5 hours or less, from magnesium, aluminum and :steel substrates, with minimum corrosion of the metal, Composition A being an immersion type stripper and Composition B a thixotropic epoxy stripper.

9 Composition B Percent by weight Parafiin wax 2.0 Microcrystalline wax 0.10 Methylene chloride 70.15 Methocel 1.75 Petronate HL 4.0 Corrosion inhibitor 0.50

Hypophosphorous acid (50% aqueous solution) 8.0 P-hydroxy anisole 1.50

Methyl alcohol 10.0

2-ethyl hexanol 2.0

The corrosion inhibitor in Compositions A and B above can be, for example, Miranol OM-SF, Deriphat 151 or Sarkosyl 0, described above. However, other suitable corrosion inhibitors can also be used.

The presence of inhibitors such as those mentioned specifically above produce low values of corrosion on aluminum and magnesium, and the use of p-hydroxy anisole as activator together with hypophosphorous acid, results in greatly reduced stripping time according to the invention. The stripping Compositions A and B above are also stable over relatively long periods, for example 2 to 4 months or longer, so that they can be stored in suitable containers for such periods substantially without loss of effectiveness.

Although the invention has been described primarily in relation to the stripping of epoxy coatings, the invention compositions can also be used for removal of other types of coating systems such as phenolics and aminealdehyde condensation products, for example.

From the foregoing, it is seen that the invention provides a novel composition and process for stripping obdurate coatings, particularly those which have heretofore been the most diificult types to remove, such as epoxy coatings, in a substantially shorter period of time as compared to conventional formulations for this purpose, and such compositions can be designed to cause relatively minor corrosion of the substrate during the stripping period, particularly where aluminum or magnesium is used for this purpose.

While we have described particular embodiments of our invention for the purpose of illustration, it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention as set forth in the appended claims.

We claim:

1. A coating remover composition consisting essentially of about 40 to about 80% by weight of methylene chloride, about 0.25 to about 15% by weight of hypophosphorous acid, and about 0.25 to about by weight of an alkyl phosphite containing from 2 to 3 alkyl chains, each such alkyl chain containing from 1 to about 8 carbon atoms.

2. A coating remover composition consisting essentially of about 40 to about 80% by weight of a chlorinated hydrocarbon liquid solvent, about 0.25 to about by weight of hypophosphorous acid, and about 0.25 to about 10% by weight of an organic compound having the general formula Where X is a member of the group consisting of ECOH, ECOCH3, EC-COOH and --O radicals.

3. A coating remover composition consisting essentially of about 40 to about 80% by weight of a chlorinated hydrocarbon liquid solvent, about 0.25 to about 15 by weight of hypophosphorous acid, and about 0.25 to about 10% by Weight of an organic compound of the group 10 consisting of p-hydroxy anisole, salicylic acid, hydroquinone, resorcinol and kojic acid.

4. A coating remover composition consisting essentially of about 40 to about by weight of a chlorinated hydrocarbon liquid solvent, about 0.25 to about 15% by weight of hypophosphorous acid and about 0.25 to about 10% by weight of p-hydroxy anisole.

5. A coating remover composition consisting essentially of about 40 to about 80% by weight of a chlorinated hydrocarbon liquid solvent, about 0.25 to about 15% by weight of hypophosphorous acid, and about 0.25 to about 10% by weight of kojic acid.

6. A coating remover composition consisting essential- 1y of about 40 to about 80% by weight of a chlorinated hydrocarbon liquid solvent, about 0.25 to about 15% by weight of hypophosphorous acid, and about 0.25 to about 10% by Weight of salicylic acid.

7. A coating remover composition particularly adapted for removal of coatings based on epoxy resins, consisting essentially of about 40 to about 80% by weight of a chlorinated hydrocarbon liquid solvent, about 0.25 to about 15 by weight of hypophosphorous acid, about 0.25 to about 10% by weight of an organic compound of the group consisting of p-hydroxy anisole, salicylic acid, hydroquinone, resorcinol and kojic acid, about 0.25 to about 15 by weight of water, and about 3 to about 20% by weight of a coupling agent selected from the group consisting of the lower aliphatic alcohols and their glycol ethers.

8. A coating remover composition consisting essentially of about 40 to about 80% by weight of a chlorinated hydrocarbon liquid solvent, about 0.25 to about 15% by weight of hypophosphorous acid, about 0.25 to about 10% by weight of an organic compound of the group consisting of p-hydroxy anisole, salcylic acid, hydroquinone, resorcinol and kojic acid, 0.25 to about 15% by weight of water, about 3 to about 20% by weight of a coupling agent selected from the group consisting of the lower aliphatic alcohols and their glycol ethers, and about 0.1 to about 2% by weight of an organic corrosion inhibitor.

9. A coating remover composition consisting essentially of about 40 to about 80% by weight of a chlorinated hydrocarbon liquid solvent, about 0.25 to about 15% by weight of hypophosphorous acid, about 0.25 to about 10% by weight of an organic compound of the group consisting of p-hydroxy anisole, salicylic acid, hydroquinone, resorcinol and kojic acid, about 0.25 to about 15% by weight of water, about 3 to about 20% by weight of a coupling agent selected from the group consisting of the lower aliphatic alcohols and their glycol ethers, about 0.1 to about 2% by weight of an organic corrosion inhibitor selected from the group consisting of oleyl ethyl cycloimidinium l-hydroxy, 3-ethyl sodium alcoholate, Z-methyl sodium carboxylate; N-alkyl amino sodium propionate, the alkyl group containing from 12 to 14 carbon atoms; and oleyl sarcosine, about 2 to about 10% by weight of a surface active agent of the group consisting of petroleum sulfonates and alkyl aryl sulfonates, and about 0.1 to about 3% by weight of a wax selected from the group consisting of paraffin wax and microcrystalline Wax as an evaporation retardant.

10. A coating remover composition consisting essentially of about 40 to about 80% by weight of a chlorinated hydrocarbon liquid solvent, about 0.25 to about 15% by weight of hypophosphorous acid, about 0.25 to about 10% by weight of p-hydroxy anisole, about 0.25 to about 15% by weight of water, about 3 to about 20% of a coupling agent of the group consisting of the lower aliphatic alcohols and their glycol ethers, about 0.1 to about 2% by weight of an organic corrosion inhibitor selected from the group consisting of oleyl ethyl cycloimidinium l-hydroxy, 3-ethyl sodium alcoholate, 2- methyl sodium carboxylate; N-alkyl amino sodium propionate, the alkyl group containing from 12 to 14 car- 11 bon atoms; and oleyl sarcosine, and about 2 to about 10% by weight of a surface active agent of the group consisting of petroleum sulfonates and alkyl aryl sulfonates.

11. A coating remover composition particularly adapted for removal of coatings based on epoxy resins, consisting essentially of about 40 to about 80% by weight of methylene chloride, about 0.25 to about 15% by weight of hypophosphorous acid, about 0.25 to about 10% by weight of p-hydroxy anisole, about 0.25 to about 15% by weight of water, and about 3 to about 20% by weight of methanol.

12. A coating remover composition particularly adapted for removal of coatings based on epoxy resins, consisting essentially of about 50 to about 70% by weight of methylene chloride, about 0.1 to about 10% by weight of hypophosphorous acid, about 0.25 to about 3% by weight of p-hydroxy anisole, about 0.25 to about by weight of water, about 5 to about 15% by weight of methanol, about 0.1 to about 2% of an organic corrosion inhibitor selected from the group consisting of oleyl ethyl cycloimidinium l-hydroxy, 3-ethyl sodium alcoholate, Z-methyl sodium carboxylate; N-alkyl amino sodium propionate, the alkyl group containing from 12 to 14 carbon atoms; and oleyl sarcosine, about 2 to about by weight of a surface active agent of the group consisting of petroleum sulfonates and alkyl aryl sulfonates, and about 0.1 to about 3% by weight of a wax selected from the group consisting of parafiin wax and microcrystalline wax as an evaporation retardant.

13. A coating remover composition consisting essentially of about 40 to about 80% by weight of a chlorinated hydrocarbon liquid solvent, about 0.25 to about 15% by weight of hypophosphorous acid, about 0.25 to about 10% by weight of an organic activator for hypophosphorous acid, selected from the group consisting of alkyl phosphites containing from 2 to 3 alkyl chains, each such alkyl chain containing from 1 to about 8 carbon atoms, and an organic compound of the group consisting of p-hydroxy anisole, salicylic acid, hydroquinone, resorcinol and kojic acid.

14. A coating remover composition consisting essentially of about to about by weight of a chlorinated hydrocarbon liquid solvent, about 1 to about 10% by weight of hypophosphorous acid, and about 0.25 to about 3% by weight of an organic activator for hypophosphorous acid, selected from the group consisting of alkyl phosphites containing from 2 to 3 alkyl chains, each such alkyl chain containing from 1 to about 8 carbon atoms, and an organic compound of the group consisting of p-hydroxy anisole, salicylic acid, hydroquinone, resorcinol and kojic acid.

15. A coating remover composition as defined in claim 13, said chlorinated hydrocarbon liquid solvent being methylene chloride.

References Cited in the file of this patent UNITED STATES PATENTS 2,507,985 Kuentzel May 16, 1950 2,528,378 Mannheimer Oct. 31, 1950 2,852,471 Atkins et a1. Sept. 16, 1958 OTHER REFERENCES Lesser, Paint Remover, Sanitary Chemicals, pages 133-136 and 161, February 1953.

McCutcheon, Surfactants Listed, Soap and Chemical Specialties, 4th revision (page 50, January 1958, and page 65, March 1958).

The Condensed Chemical Dictionary, 5th ed. (1956), pages 574, 581, 942 and 958, Reinhold Publishing Co.

The Merck Index, 6th edition (1952), page 441. 

1. A COATING REMOVER COMPOSITION CONSISTING ESSENTIALLY OF ABOUT 40 TO ABOUT 80% BY WEIGHT OF METHYLENE CHLORIDE, ABOUT 0.25 TO ABOUT 15% BY WEIGHT OF HYPOPHOSPHOROUS ACID, AND ABOUT 0.25 TO ABOUT 10% BY WEIGHT OF AN ALKYL PHOSPHITTE CONTAINING FROM 2 TO 3 ALKYL CHAINS, EACH SUCH ALKYL CHAIN CONTAINING FROM 1 TO ABOUT 8 CARBON ATOMS.
 7. A COATING REMOVER COMPOSITION PARTICULARLY ADAPTED FOR REMOVAL OF COATINGS BASED ON EPOXY RESINS, CONSISTING ESSENTIALLY OF ABOUT 40 TO ABOUT 80% BY WEIGHT OF A CHLORINATED HYDROCARBON LIQUID SOLVENT, ABOUT 0.25 TO ABOUT 15% BY WEIGHT OF HYDROPHOSPHOROUS ACID, ABOUT 0.25 TO ABOUT 10% BY WEIGHT OF AN ORGANIC COMPOUND OF THE GROUP CONSISTING OF P-HYDROXY ANISOLE, SALICYLIC ACID, HYDROQUINONE, RESORCINOL AND KOJIC ACID, ABOUT 0.25 TO ABOUT 15% BY WEIGHT OF WATER, AND ABOUT 3 TO ABOUT 20% BY WEIGHT OF A COUPLING AGENT SELECTED FROM THE GROUP CONSISTING OF THE LOER ALIPHATIC ALCOHOL AND THEIR GLYCOL ETHERS. 